The prevent invention relates to apparatus for producing tubular fabrics consisting of a number of separate chain stitches connected by an inlaid thread typically, elastic or similar yarn. In particular, the invention relates to a high speed yarn knitting apparatus for knitting netting for covering food products, and in particular meat.
High speed yarn knitting apparatus should satisfy a number of desirable criteria in addition to being reliable, fast and relatively inexpensive. It should permit the fabric to be continuously knitted and should require a minimal amount of space and be relatively lightweight. The supplies of yarn should be readily changed or added to without interrupting the operation of the machine and a counterweight should not be required to avoid imbalance at high speed. The high speed knitting apparatus should have yarn positioning apparatus which uses a minimal number of moving parts and wear and tear of knitting elements and yarn should also be minimised. Higher tensions of yarn should be obtainable so that knitting speeds can be increased. The apparatus should also minimise the splitting of yarn and the dropping of stitches.
Prior art knitting machines are of two general types. The first type consists of a machine which can make several rolls at a single time using a reciprocal movement. However, this machine is large and the reciprocal movement is very slow, thus limiting the amount of rolls of knitted fabric which can be produced in a certain time. The second type of machine uses a circular movement, however, this produces only a single roll at a time and the size of the yarn package limits the amount of continuous netting which can be made without stopping. The yarn package is mounted to rotate with the cambox which means that the speed of rotation and hence knitting is limited. Also, when the weft package is empty the machine must be stopped, reset and retensioned before it can then operate. This takes time and the overall speed of the machine is relatively slow. In addition, because the package rotates, a counterweight is required for balance, which is heavy, and also requires space within the machine which results in the overall machine taking up a relatively large area.
Existing circular knitting machines which are also designed to make a chain stitch structure use one of two generally accepted methods of supplying yarn to the needles of the knitting head. One method uses rotating or reciprocating guides which wrap the yarn around the needles. The elastic or other weft yarn is fed from the outside and is laid between the needles from the outside. This requires the weft yarn package to rotate with the cam box. In another method, stationary guides are present and rely on being struck by the needles so as to deflect the needles behind the yarn. The yarn is then caught by the open hook of the needle as the needle descends. Again, the weft yarn package revolves with the cam box.
These existing methods have a number of problems. The former method uses reciprocating guides requiring a machine which is relatively complicated and uses a considerable number of moving parts. In the second method, as the needles strike the guides there is considerable wear and tear on both the needles and the guides. This can cause splitting of the yarn and dropping of stitches as well as broken knitting elements.
An object of the present invention is to provide an improved knitting apparatus and yarn tensioning apparatus which obviates or mitigates the aforesaid disadvantages. This is achieved by providing a high speed knitting apparatus in which the elastic thread packages are mounted in a stationary position away from the knitting head and the yarn is fed from the exterior to the inside of each knitting head. Yarn is laid down outside each needle as the needle rises but falls behind the needle as the stitch is made allowing a stationary package. This results in reducing the revolving mass and the space necessary to accommodate the revolving mass. Furthermore, since the weft package is stationary, the commencement of wind on the package can be left as a tail which is knotted to the free end of a second package thus permitting the machine to run continuously without stopping to change packages.
A yarn guide is included for each needle of the knitting head so that yarn is moved under tension within the guide by a rotating member with minimal friction to a position where the needle will trap the yarn on its downward stroke.
This arrangement also permits a plurality of like knitting heads to be mounted in relatively close proximity in a single machine frame in such a manner that chain stitches can be fed from a power driven warp beam.
In a preferred arrangement, a plurality of knitting heads are mounted on a knitting head frame fed from a single warp and stationary creels can be mounted at the sides of the frame for supplying weft yarn to respective knitting heads. The knitting head frame can also include a fabric take-off roll for receiving the knitted fabric from each of the knitting heads. In an alternative arrangement the knitting heads may be mounted on a frame fed by a plurality of warps.
Each knitting head consists of a hollow cylinder having a plurality of grooves called tricks, in the outer wall, in which needles are disposed. Fixed feeders are disposed above the cylinder to offer the warp yarns to the needle. Disposed between the cylinder and the fixed feeder is a rotating weft feeder and yarn deflector. Rotation of the feeder is synchronized with a cam which raises the needles so that the feeder deflects the warp yarn within the yarn guide and guides and lays the elastic weft yarn outside the needle so that as the needle rises and falls the rubber yarn is trapped between the chain stitches and falls behind the needle as a stitch is made, in a spiral fashion to provide radial and circumferential elasticity or rigidity in the knitted fabric.
The fixed feeders are mounted radially in the supported feeder head support tube through which passes a tube mounted in bearings and carrying the weft feeder and deflector so that these can be rotated by a synchronised drive while feeding the inlay weft thread. The fixed feeders are wire staples which are shaped so that pre-tensioning of the yarn before it reaches the guide ensures that the yarn lies in front of and to one side of the open hook of the needle, and limits yarn movement when contacted with the placer. The staple has a curved portion for defining the path of the yarn as it is moved. The placer is a planar element which has a curved portion which pushes the yarn along the internal rim of the feeder from a first position to a second position where the yarn is trapped.
Accordingly, in one aspect of the present invention there is provided a knitting head for use with a knitting machine said knitting head comprising:
a fixed hollow cylinder having a cylinder wall with a plurality of circumferentially spaced grooves disposed in said wall, each groove having a needle with a hook at its upper end disposed therein,
said hollow cylinder being disposed in a cam box having rotary cam means adapted to be coupled to each needle so that rotation of said rotary cam means causes displacement of each needle along its respective groove,
stationary warp yarn delivery means disposed above said hollow cylinder for feeding a warp yarn from a remote location to each respective needle,
rotatable weft yarn delivery means disposed between said hollow cylinder and said stationary warp yarn delivery means for delivering a weft yarn from a remote location outside the cylinder and from the inside to the outside of said rotatable weft delivery means so that the weft yarn is laid on the outside of each successively rising needle,
the speed of rotation of said rotary cam means and said rotatable weft yarn delivery means being synchronised whereby in use, upon rotation of said rotary cam means and said rotatable weft yarn delivery means displacement of said needles causes chain stitches to be made which are fed inside said cylinder, and said rotatable weft yarn delivery means delivers said weft yarn outside said needle as said needles rise and the tension in said weft yarn pulls it over the top of the needle when it descends to be trapped in a subsequent stitch which falls behind the needle as the stitch is made, said rotatable weft yarn delivery means comprising a generally planar horizontal weft yarn rotatable feeder and deflector element, said rotatable feeder and deflector element being coupled to a rotatable hollow yarn delivery tube driven by drive means, said tube and said rotating feeder and deflector having passage means through which a weft thread can be fed to be disposed outside the periphery of the hollow cylinder, the deflector including an outer cam portion for deflecting the warp yarn outside the periphery of the hollow cylinder as said deflector rotates.
Preferably, said needle includes a pivotable latch for preventing said weft yarn from being hooked by said needle on a downward stroke. Conveniently, said grooves are disposed in an outer wall of said hollow cylinder and said needle hooks face outwardly.
Preferably also, the knitting head and needle grooves are generally vertically disposed and the warp yarn is fed to said knitting head in a generally vertical direction.
Conveniently, said rotatable weft yarn delivery means comprises a generally planar horizontal weft yarn rotatable feeder and deflector element, said rotatable feeder and deflector element being coupled to a rotatable hollow yarn delivery tube which is adapted to be driven by drive means, said tube and said rotating feeder and deflector having passage means through which a weft thread can be fed to be disposed outside the needles as they rise. Conveniently, the deflector includes an outer cam portion for deflecting the warp yarn outside the periphery of the hollow cylinder as said deflector rotates.
Accordingly, in another aspect of the invention there is provided a knitting machine comprising:
warp yarn delivery means for delivering a plurality of warp yarns to at least one knitting head, said knitting head being disposed in a knitting head frame and the knitting head receiving a plurality of warp yarns, said knitting head frame having a plurality of weft yarn package holders disposed at a remote position from said knitting head, at least one package holder being adapted to supply said at least one knitting head with weft yarn, and a fabric take-off roll disposed in said knitting head frame for receiving knitted fabric from said knitting machine, said rotating weft yarn delivery means comprising a generally planar horizontal weft yarn rotatable feeder and deflector element, said rotatable feeder and deflector element being coupled to a rotatable hollow yarn delivery tube driven by drive means, said tube and said rotating feeder and deflector element having passage means through which a weft thread can be fed to be disposed outside the knitting head, the deflector element including an outer cam portion for deflecting the warp yarn outside the periphery of the knitting head as said deflector element rotates.
Conveniently, said knitting machine has a plurality of knitting heads and said warp is driven by warp drive rollers and said warp yarn is fed across to said knitting head frame via a warp sheet. Conveniently also, yarn tensioning devices are provided for controlling the tension of each yarn fed to respective knitting heads.
Alternatively said knitting machine has a single head and said warp yarn is fed to said single head from a creel having a plurality of package holders.
Accordingly, in yet another aspect of the invention there is yet provided a method of knitting a tubular fabric using the knitting head as defined above comprising the steps: feeding a plurality of warp yarn threads to a knitting head; feeding at least one weft yarn inside said knitting head from a remote location outside said knitting head; passing the weft yarn from the inside to the outside of said knitting head and disposing said weft initially around the periphery of said knitting head by a rotary movement outside said needles as they arise, and synchronising the movement of needles with respect to the rotating weft yarn delivery means within said knitting head to cause the weft yarn disposed around the periphery of said knitting head to be trapped between successive stitches of said warp yarn and to fall behind the needle as a stitch is made to create a tubular structure  comprising the steps of feeding a plurality of warp yarn threads to a knitting head including vertically moveable needles, said knitting head including an inside and an outside, feeding at least one weft yarn inside said knitting head from a remote location outside the knitting head, delivering the weft yarn from the inside to the outside of said knitting head by a rotatable weft yarn delivery means comprising a generally planar horizontal weft yarn rotatable feeder and deflector element, said rotatable feeder and deflector element being coupled to a rotatable hollow yarn delivery tube driven by drive means, said tube and said rotating feeder and deflector element having passage means through which a weft thread is fed and disposing said weft yarn initially on the outside of said knitting head by a rotary movement of an outer cam portion of said deflector element to lay the weft yarn outside said needles as the needles rise, synchronizing movement and displacement of needles with respect to the delivery of the weft yarn to cause the weft yarn disposed around the outside of said knitting head to be trapped between successive stitches of said warp yarn and to fall behind the needle as a stitch is made to create a tubular structure.
Conveniently, said method includes the step of feeding the warp and weft yarns from a remote stationary location. Preferably said warp yarns are fed vertically downwards to vertically disposed knitting heads.
Conveniently also, two weft package holders are provided for each knitting head and the package holders are adapted to be tied together to provide substantially continuous knitting by each knitting head to produce a continuous tubular fabric.
According to yet another aspect of the present invention there is provided warp yarn positioning apparatus when used in a high speed knitting apparatus comprising a knitting head having a plurality of needles, each of said needles being movable in a needle trick, said warp yarn positioning apparatus comprising a plurality of warp yarn guides each guide defining an aperture for receiving a respective warp yarn passing therethrough and for containing and controlling movement of each of said warp yarns, each warp yarn guide being mounted above a respective needle, at least one yarn deflecting means being adapted to rotate around said knitting head for engaging said warp yarn and for deflecting said yarns across said apertures from a first position to a second position such that, in said second position, each of said yarns is trapped by its respective needle as it descends.
Preferably, said guide is a hardened wire staple.
Conveniently, each of said guides are mounted in a common place on a shallow, cylindrical stationary dial, said dial being disposed above said knitting head.
Preferably also, said yarn deflecting means is a planar placing element, said planar placing element being movable around said knitting head and passing above each of said guides. Alternatively, the placing element can pass beneath the shaped aperture.
Conveniently, a plurality of placing elements are mounted on an elongate member connected to a cam box, said placing elements being associated with a cam of said cam box and said cam box being rotatable around said stationary dial.
These and other aspect of the invention will become apparent from the following description when taken in combination with the accompanying drawings in which:
FIG. 1 is a diagrammatic and perspective view of a knitting machine consisting of a plurality of knitting heads in accordance with an embodiment of the invention;
FIG. 2 is a plan view of a knitting head of the knitting machine shown in FIG. 1;
FIG. 3 is a front elevation of the knitting head shown in FIG. 2;
FIG. 4 is an enlarged view of part of the knitting head shown in FIG. 2;
FIG. 5a, 5b are diagrammatic elevational views of the knitting head showing the operation of the apparatus in accordance with the embodiment of the present invention;
FIG. 6 depicts part of a net knitted with a knitting head shown in FIGS. 7, 8, and 9a-9g;
FIG. 7 is an enlarged said elevation of a knitting head in accordance with an alternative embodiment of the invention;
FIG. 8 is a plan view taken on the lines 3xe2x80x943 of FIG. 7 and depicting the shape of the weft yarn feeder and deflector, and
FIGS. 9a to g depict sequential stages in the knitting of a tubular fabric by the knitting head in accordance with the second embodiment of the present invention.